Flow control protocol

ABSTRACT

A method and apparatus for processing message is described. In one embodiment, an application programming interface is configured for receiving and sending messages. A message credit account of a sender is maintained. The message credit account of the sender is debited when a message is received from the sender to a receiver. The message credit account of the sender is credited when a replenishment message is sent to the sender in response to the receiver processing the received message. The sender is prevented from sending any messages to the receiver when a balance in the message credit account of the sender becomes negative.

TECHNICAL FIELD

Embodiments of the present invention relate to group communication, andmore specifically to processing of messages.

BACKGROUND

Group communication protocol designed for multicast communication may beused to communicate messages between endpoints forming a group.Communication endpoints can be processes or objects, or any entity thatcan send and receive messages to/from a group.

However, messages from different senders are conventionally processed ina First In First Out (FIFO) order in a single queue for incomingmessages by one thread. The messages are processed sequentially in theorder they are received. A bottleneck may thus be formed since everymessage has to wait for its turn to be processed accordingly.

Further, a situation may arise where a sender sends messages at a ratemuch faster than a receiver receiving and processing messages. Thesender may deluge a receiver with messages. In this situation, thereceiver must buffer the messages and may run out of memory.

DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in which:

FIG. 1 illustrates a network architecture of a group communication inwhich embodiments of the present invention may be implemented.

FIG. 2 illustrates a block diagram of one embodiment of a structure of amessage.

FIG. 3 illustrates a block diagram of one embodiment of channel states.

FIG. 4 illustrates a block diagram of one embodiment of a concurrentstack.

FIG. 5 illustrates a block diagram of an exemplary computer system.

FIG. 6 illustrates a flow diagram of one embodiment of a method foradjusting a flow control of processing messages.

FIG. 7 illustrates a table of properties for a flow control protocol inaccordance with one embodiment.

DETAILED DESCRIPTION

Described herein is a method and apparatus for processing messages usinga flow control protocol. The flow control protocol adjusts the rate atwhich a sender may send messages based on a message credit account ofthe sender.

In the following description, numerous details are set forth. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without these specific details. In some instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention.

Some portions of the detailed descriptions which follow are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any typeof media suitable for storing electronic instructions, and each coupledto a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein.

A machine-accessible storage medium includes any mechanism for storingor transmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-accessible storage medium includesread only memory (“ROM”); random access memory (“RAM”); magnetic diskstorage media; optical storage media; flash memory devices; electrical,optical, acoustical or other form of propagated signals (e.g., carrierwaves, infrared signals, digital signals, etc.); etc.

Group Communication Architecture

FIG. 1 illustrates an exemplary network architecture of a groupcommunication 100, such as JGroups, in which embodiments of the presentinvention may operate.

JGroups is toolkit for reliable group communication. Processes can joina group, send messages to all members or single members and receivemessages from members in the group. The system keeps track of themembers in every group, and notifies group members when a new memberjoins, or an existing member leaves or crashes. A group is identified byits name. Groups do not have to be created explicitly; when a processjoins a non-existing group, that group will be created automatically.Member processes of a group can be located on the same host, within thesame LAN, or across a WAN. A member can be part of multiple groups.

The group communication architecture may comprise three parts: (1) achannel API 106 used by application programmers to build reliable groupcommunication applications, (2) building blocks 108, which are layeredon top of channel 106 and provide a higher abstraction level and (3) aprotocol stack 104, which implements the properties specified for agiven channel.

Channel 106 is connected to protocol stack 104. Whenever an applicationsends a message, channel 106 passes it on to protocol stack 104comprising several protocols 112, 114, 116, 118, 120. The topmostprotocol processes the message and the passes it on to the protocolbelow it. Thus, the message is handed from protocol to protocol untilthe bottom protocol puts it on the network 102. The same happens in thereverse direction: the bottom (transport) protocol listens for messageson network 102. When a message is received, it will be handed upprotocol stack 104 until it reaches channel 106. Channel 106 stores themessage in a queue until application 110 consumes it.

When an application 110 connects to a channel 106, protocol stack 106will be started, and when it disconnects protocol stack 104 will bestopped. When the channel 106 is closed, the stack 140 will bedestroyed, releasing its resources.

Channel

To join a group and send messages, a process has to create a channel andconnect to it using the group name (all channels with the same name forma group). The channel is the handle to the group. While connected, amember may send and receive messages to/from all other group members.The client leaves a group by disconnecting from the channel. A channelcan be reused: clients can connect to it again after havingdisconnected. However, a channel may allow only one client to beconnected at a time. If multiple groups are to be joined, multiplechannels can be created and connected to. A client signals that it nolonger wants to use a channel by closing it. After this operation, thechannel may not be used any longer.

Each channel has a unique address. Channels always know who the othermembers are in the same group: a list of member addresses can beretrieved from any channel. This list is called a view. A process canselect an address from this list and send a unicast message to it (alsoto itself), or it may send a multicast message to all members of thecurrent view. Whenever a process joins or leaves a group, or when acrashed process has been detected, a new view is sent to all remaininggroup members. When a member process is suspected of having crashed, asuspicion message is received by all non-faulty members. Thus, channelsreceive regular messages, view messages and suspicion messages. A clientmay choose to turn reception of views and suspicions on/off on a channelbasis.

Channels may be similar to BSD sockets: messages are stored in a channeluntil a client removes the next one (pull-principle). When no message iscurrently available, a client is blocked until the next availablemessage has been received.

A channel may be implemented over a number of alternatives for grouptransport. Therefore, a channel is an abstract class, and concreteimplementations are derived from it, e.g. a channel implementation usingits own protocol stack, or others using existing group transports suchas Jchannel and EnsChannel. Applications only deal with the abstractchannel class, and the actual implementation can be chosen at startuptime.

The properties for a channel may be specified in a colon-delimitedstring format. When creating a channel (JChannel) a protocol stack willbe created according to these properties. All messages will pass throughthis stack, ensuring the quality of service specified by the propertiesstring for a given channel.

Building Blocks

Channels are simple and primitive. They offer the bare functionality ofgroup communication, and have on purpose been designed after the simplemodel of BSD sockets, which are widely used and well understood. Thereason is that an application can make use of just this small subset ofJGroups, without having to include a whole set of sophisticated classes,that it may not even need. Also, a somewhat minimalistic interface issimple to understand: a client needs to know about 12 methods to be ableto create and use a channel (and oftentimes will only use 3-4 methodsfrequently).

Channels provide asynchronous message sending/reception, somewhatsimilar to UDP. A message sent is essentially put on the network and thesend( ) method will return immediately. Conceptual requests, orresponses to previous requests, are received in undefined order, and theapplication has to take care of matching responses with requests.

Also, an application has to actively retrieve messages from a channel(pull-style); it is not notified when a message has been received. Notethat pull-style message reception often needs another thread ofexecution, or some form of event-loop, in which a channel isperiodically polled for messages.

JGroups offers building blocks that provide more sophisticated APIs ontop of a Channel. Building blocks either create and use channelsinternally, or require an existing channel to be specified when creatinga building block. Applications communicate directly with the buildingblock, rather than the channel. Building blocks are intended to save theapplication programmer from having to write tedious and recurring code,e.g. request-response correlation.

Protocol Stack

As discussed above, JGroups provides two channel implementations: anEnsemble-based channel and its own channel based on a Java protocolstack. The latter is a protocol stack containing a number of protocollayers in a bidirectional list. FIG. 1 illustrates protocol stack 104with the following protocols: CAUSAL 112, GMS 114, MERGE 116, FRAG 118,UDP 120.

All messages sent and received over the channel have to pass through theprotocol stack. Every layer may modify, reorder, pass or drop a message,or add a header to a message. A fragmentation layer might break up amessage into several smaller messages, adding a header with an id toeach fragment, and re-assemble the fragments on the receiver's side.

The composition of the protocol stack, i.e. its layers, is determined bythe creator of the channel: a property string defines the layers to beused (and the parameters for each layer). This string might beinterpreted differently by each channel implementation; in JChannel itis used to create the stack, depending on the protocol names given inthe property.

Knowledge about the protocol stack is not necessary when only usingchannels in an application. However, when an application wishes toignore the default properties for a protocol stack, and configure theirown stack, then knowledge about what the individual layers are supposedto do is needed. Although it is syntactically possible to stack anylayer on top of each other (they all have the same interface), thiswouldn't make sense semantically in most cases.

Message

Data is sent between members in the form of messages. A message can besent by a member to a single member, or to all members of the group ofwhich the channel is an endpoint. An example of a structure of a message200 is illustrated in FIG. 2.

The message 200 may contain five fields: headers 202, destinationaddress 204, source address 206, flags 208, and payload 210.

A list of headers 202 can be attached to a message. Anything that shouldnot be in the payload 210 can be attached to message 200 as a header.Methods putHeader( ), getHeader( ), and removeHeader( ) of message 200can be used to manipulate headers 202.

The destination address 204 may include the address of the receiver. Ifnull, the message will be sent to all current group members.

The source address 206 may include the address of a sender. It can beleft null, and will be filled in by the transport protocol (e.g. UDP)before the message is put on the network 102.

One byte of the message 200 may be used for flags 208. Examples of flagsmay be OOB, LOW_PRIO and HIGH_PRIO.

The payload 210 may include the actual data (as a byte buffer). Themessage class contains convenience methods to set a serializable objectand to retrieve it again, using serialization to convert the objectto/from a byte buffer.

The message 200 may be similar to an IP packet and consists of thepayload (a byte buffer) and the addresses of the sender and receiver (asaddresses). Any message put on the network 102 can be routed to itsdestination (receiver address), and replies can be returned to thesender's address.

A message usually does not need to fill in the sender's address whensending a message; this is done automatically by the protocol stackbefore a message is put on the network. However, there may be cases,when the sender of a message wants to give an address different from itsown, so that for example, a response should be returned to some othermember.

The destination address (receiver) can be an Address, denoting theaddress of a member, determined e.g. from a message received previously,or it can be null, which means that the message will be sent to allmembers of the group. A typical multicast message, sending string“Hello” to all members would look like this:

-   -   Message msg=new Message(null, null, “Hello”.getBytes( ));    -   channel.send(msg);        Channel States

A state transition diagram 300 for the major states a channel can assumeare shown in FIG. 3. In order to join a group and send messages, aprocess has to create a channel. A channel is like a socket. When aclient connects to a channel, it gives the name of the group it wouldlike to join. Thus, a channel is (in its connected state) alwaysassociated with a particular group. The protocol stack takes care thatchannels with the same group name find each other: whenever a clientconnects to a channel given group name G, then it tries to find existingchannels with the same name, and joins them, resulting in a new viewbeing installed (which contains the new member). If no members exist, anew group will be created.

When a channel is first created at 308, it is in the unconnected state302. An attempt to perform certain operations which are only valid inthe connected state (e.g. send/receive messages) will result in anexception. After a successful connection by a client, it moves to theconnected state 304. Now channels will receive messages, views andsuspicions from other members and may send messages to other members orto the group. Getting the local address of a channel is guaranteed to bea valid operation in this state (see below). When the channel isdisconnected, it moves back to the unconnected state 302. Both aconnected and unconnected channel may be closed 306, which makes thechannel unusable for further operations. Any attempt to do so willresult in an exception. When a channel is closed directly from aconnected state, it will first be disconnected, and then closed.

Concurrent Stack

The architecture 400 of one embodiment of a concurrent stack 405 isshown in FIG. 4. As previously discussed, channel 406 communicate withtransport protocol 404 to a network 402. However, transport protocol 404may include the following protocols: TP, with subclasses UDP, TCP andTCP_NIO. Therefore, to configure the concurrent stack, the user has tomodify the config for (e.g.) UDP in the XML file.

Concurrent stack 405 consists of two thread pools: an out-of-band (OOB)thread pool 414 and a regular thread pool 416. Packets are received fromMulticast receiver 408, Unicast receiver 410, or a Connection Table 412(TCP, TCP_NIO). Packets marked as OOB (withMessage.setFlag(Message.OOB)) are dispatched to the OOB thread pool 414,and all other packets are dispatched to the regular thread pool 416.

When a thread pool is disabled, then the thread of the caller (e.g.multicast or unicast receiver threads or the ConnectionTable) is used tosend the message up the stack and into the application. Otherwise, thepacket will be processed by a thread from the thread pool, which sendsthe message up the stack. When all current threads are busy, anotherthread might be created, up to the maximum number of threads defined.Alternatively, the packet might get queued up until a thread becomesavailable.

The point of using a thread pool is that the receiver threads shouldonly receive the packets and forward them to the thread pools forprocessing, because unmarshalling and processing is slower than simplyreceiving the message and can benefit from parallelization.

Previously, all messages received were processed by a single thread,even if the messages were sent by different senders. For instance, ifsender A sent messages 1,2 and 3, and B sent message 34 and 45, and ifA's messages were all received first, then B's messages 34 and 35 couldonly be processed after messages 1-3 from A were processed.

Now, messages from different senders can be processed in parallel, e.g.messages 1, 2 and 3 from A can be processed by one thread from thethread pool and messages 34 and 35 from B can be processed on adifferent thread.

As a result, a speedup of almost N for a cluster of N if every node issending messages may be obtained. The thread pool may be configured tohave at least N threads.

Computer System

FIG. 5 illustrates a diagrammatic representation of a machine in theexemplary form of a computer system 500 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies discussed herein, may be executed. In alternativeembodiments, the machine may be connected (e.g., networked) to othermachines in a LAN, an intranet, an extranet, or the Internet. Themachine may operate in the capacity of a server or a client machine inclient-server network environment, or as a peer machine in apeer-to-peer (or distributed) network environment. The machine may be apersonal computer (PC), a tablet PC, a set-top box (STB), a PersonalDigital Assistant (PDA), a cellular telephone, a web appliance, aserver, a network router, switch or bridge, or any machine capable ofexecuting a set of instructions (sequential or otherwise) that specifyactions to be taken by that machine. Further, while only a singlemachine is illustrated, the term “machine” shall also be taken toinclude any collection of machines that individually or jointly executea set (or multiple sets) of instructions to perform any one or more ofthe methodologies discussed herein.

The exemplary computer system 500 includes a processing device 502, amain memory 504 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) such as synchronous DRAM (SDRAM) or RambusDRAM (RDRAM), etc.), a static memory 506 (e.g., flash memory, staticrandom access memory (SRAM), etc.), and a data storage device 518, whichcommunicate with each other via a bus 530.

Processing device 502 represents one or more general-purpose processingdevices such as a microprocessor, central processing unit, or the like.More particularly, the processing device may be complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,or processor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processing device 502may also be one or more special-purpose processing devices such as anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), a digital signal processor (DSP), network processor,or the like. The processing device 502 is configured to execute theprocessing logic 526 for performing the operations and steps discussedherein.

The computer system 500 may further include a network interface device508. The computer system 500 also may include a video display unit 510(e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), analphanumeric input device 512 (e.g., a keyboard), a cursor controldevice 514 (e.g., a mouse), and a signal generation device 516 (e.g., aspeaker).

The data storage device 518 may include a machine-accessible storagemedium 530 on which is stored one or more sets of instructions (e.g.,software 522) embodying any one or more of the methodologies orfunctions described herein. The software 522 may also reside, completelyor at least partially, within the main memory 504 and/or within theprocessing device 502 during execution thereof by the computer system500, the main memory 504 and the processing device 502 also constitutingmachine-accessible storage media. The software 522 may further betransmitted or received over a network 520 via the network interfacedevice 508.

The machine-accessible storage medium 530 may also be used to JGroupsand concurrent stack configurations 524. JGroups and concurrent stackconfigurations 524 may also be stored in other sections of computersystem 500, such as static memory 506.

While the machine-accessible storage medium 530 is shown in an exemplaryembodiment to be a single medium, the term “machine-accessible storagemedium” should be taken to include a single medium or multiple media(e.g., a centralized or distributed database, and/or associated cachesand servers) that store the one or more sets of instructions. The term“machine-accessible storage medium” shall also be taken to include anymedium that is capable of storing, encoding or carrying a set ofinstructions for execution by the machine and that cause the machine toperform any one or more of the methodologies of the present invention.The term “machine-accessible storage medium” shall accordingly be takento include, but not be limited to, solid-state memories, optical andmagnetic media, and carrier wave signals.

Flow Control

Flow Control (FC) takes care of adjusting the rate of a message senderto the rate of the slowest receiver over time. If a sender continuouslysends messages at a rate that is faster than the receiver(s), thereceivers will either queue up messages, or the messages will getdiscarded by the receiver(s), triggering costly retransmissions. Inaddition, there is spurious traffic on the cluster, causing even moreretransmissions. Thus, Flow control throttles the sender so thereceivers are not overrun with messages.

FC uses a credit based system, where each sender has max_credits creditsand decrements them whenever a message is sent. The sender blocks whenthe credits fall below 0, and only resumes sending messages when itreceives a replenishment message from the receivers.

The receivers maintain a table of credits for all senders and decrementthe given sender's credits as well, when a message is received. FIG. 7illustrates an example of a table of properties. When a sender's creditsdrops below a threshold, the receiver will send a replenishment messageto the sender. The threshold is defined by min_bytes or min_threshold.

In accordance with another embodiment, in a simplified version of FC, FCcan actually still overrun receivers when the transport's latency isvery small. SFC is a simple flow control protocol for group(=multipoint) messages.

Every sender has max_credits bytes for sending multicast messages to thegroup.

Every multicast message (we don't consider unicast messages) decrementsmax_credits by its size. When max_credits falls below 0, the sender asksall receivers for new credits and blocks until all credits have beenreceived from all members.

When the receiver receives a credit request, it checks whether it hasreceived max_credits bytes from the requester since the last creditrequest. If yes, it sends new credits to the requester and resets themax_credits for the requester. Else, it takes a note of the creditrequest from P and—when max_credits bytes have finally been receivedfrom P—it sends the credits to P and resets max_credits for P.

The maximum amount of memory for received messages is therefore <numberof senders>*max_credits.

The relationship with STABLE is as follows: when a member Q is slow, itwill prevent STABLE from collecting messages above the ones seen by Q(everybody else has seen more messages). However, because Q will *not*send credits back to the senders until it has processed all messagesworth max_credits bytes, the senders will block. This in turn allowsSTABLE to progress and eventually garbage collect most messages from allsenders. Therefore, SFC and STABLE complement each other, with SFCblocking senders so that STABLE can catch up.

FIG. 6 is a flow diagram illustrating a computer-implemented method forprocessing messages. A flow control application protocol may be writtenin Java to provide reliable multicast communication. At 602, a messagecredit account of a sender is maintained. At 604, the message creditaccount of the sender is debited when the sender sends a message. At606, the message credit account of the sender is credited when therecipient receives and processes a message. At 608, the sender isprevented from sending any messages when the balance of the messagecredit account is negative.

Thus, a method and apparatus for processing messages has been described.It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A computer-implemented method comprising: maintaining, by a receiver computing device that is one of a plurality of members of a communications group, a message credit account for each member of the communications group that can send messages to the receiver computing device, wherein each message credit account tracks the number of messages sent between the receiver computing device and a member of the communications group; receiving messages from a plurality of senders that are members of the communications group, wherein the receiving messages comprise receiving packets from the plurality of senders with a transport protocol stack; forming a channel for each sender; and processing messages from each sender in parallel with the corresponding channel, wherein the processing further comprises: debiting, by the receiver computing device, a first message credit account associated with the sender when the received message is processed by the receiver computing device, wherein the sender maintains a second message credit account associated with the receiver computing device, and wherein the sender does not send messages to any member of the communications group when a balance of the second message credit account is less than or equal to zero; sending, by the receiver computing device, a replenishment message to the sender in response to a balance of the first message credit account falling below a threshold, the replenishment message to increase credits in the second message credit account of the sender so that the sender can at least one of continue or resume sending messages to members of the communications group; and sending the packets marked as Out of Band to an Out of Band thread pool.
 2. The method of claim 1 wherein the transport protocol comprising a multicast receiver thread, a unicast receiver thread, and a connection table.
 3. The method of claim 2 further comprising sending all other packets to a regular thread pool.
 4. The method of claim 3 further comprising: processing a packet with a thread from the regular thread pool.
 5. The method of claim 4 further comprising: forming another thread to process the packet when all threads from the regular thread pool are busy.
 6. The method of claim 1 wherein processing messages further comprises: processing messages for each sender with one thread from a thread pool of a transport protocol stack.
 7. The method of claim 6 wherein the thread sends the messages up the transport protocol stack to a corresponding channel of a channel layer, a building block layered on top of the channel layer, and an application programming interface layered on top of the building block.
 8. A computer-implemented method comprising: maintaining, by a sender computing device that is one of plurality of members of a communications group, a message credit account for each member of the communications group that the sender computing device can send a message, wherein each message credit account tracks the number of messages sent between the sender computing device and the member of the communications group associated with the message credit account; receiving messages from a plurality of senders that are members of the communications group, wherein the receiving message comprises receiving packets from the plurality of senders with a transport protocol stack; forming a channel for each sender; and processing messages from each sender in parallel with the corresponding channel, wherein the processing further comprises: sending a message to a receiver that is a member of the communications group; debiting a first message credit account associated with the receiver upon sending the message to the receiver, wherein the receiver maintains a second message credit account associated with the sender computing device; blocking, by the sender computing device, sending messages to any member of the communications group when a balance of the first message credit account is less than or equal to zero; receiving a replenishment message from the receiver, when a balance of the second message credit account falls below a threshold, wherein the replenishment message to increase credits in the first message credit account; resuming sending messages to any member of the communications group when the balance of the first message credit account is greater than zero; and sending the packets marked as Out of Band to an Out of Band thread pool.
 9. The method of claim 8 wherein the transport protocol comprising a multicast receiver thread, a unicast receiver thread, and a connection table.
 10. The method of claim 9 further comprising: sending all other packets to a regular thread pool.
 11. The method of claim 10 further comprising: processing a packet with a thread from the regular thread pool.
 12. The method of claim 11 further comprising: forming another thread to process the packet when all threads from the regular thread pool are busy.
 13. The method of claim 8 wherein processing messages further comprises: processing messages for each sender with one thread from a thread pool of a transport protocol stack.
 14. The method of claim 13 wherein the thread sends the messages up the transport protocol stack to a corresponding channel of a channel layer, a building block layered on top of the channel layer, and an application programming interface layered on top of the building block.
 15. A non-transitory machine-accessible storage medium including data that, when accessed by a machine, causes the machine to perform operations comprising: maintaining, by a receiver computing device that is one of a plurality of members of a communications group, a message credit account for each member of the communications group that can send messages to the receiver computing device, wherein each message credit account tracks the number of messages sent between the receiver computing device and a member of the communications group; receiving messages from a plurality of senders that are members of the communications group, wherein the receiving messages comprise receiving packets from the plurality of senders with a transport protocol stack; forming a channel for each sender; and processing messages from each sender in parallel with the corresponding channel, wherein the processing further comprises: receiving a message from a sender that is a member of the communications group; debiting a first message credit account associated with the sender when the received message is processed by the receiver computing device, wherein the sender maintains a second message credit account associated with the receiver computing device, and wherein the sender does not send messages to any member of the communications group when a credit balance of the second message credit account is less than or equal to zero; sending a replenishment message to the sender in response to the message credit account associated with the sender falling below a threshold, the replenishment message to increase credits in the second message credit account of the sender so that the sender can at least one of continue or resume sending messages to members of the communications group; and sending the packets marked as Out of Band to an Out of Band thread pool.
 16. The non-transitory machine-accessible storage medium of claim 15 wherein the transport protocol comprising a multicast receiver thread, a unicast receiver thread, and a connection table.
 17. The non-transitory machine-accessible storage medium of claim 16 further comprising: sending all other packets to a regular thread pool.
 18. A non-transitory machine-accessible storage medium including data that, when accessed by a machine, cause the machine to perform operations comprising: maintaining, by a sender computing device that is one of plurality of members of a communications group, a message credit account for each member of the communications group that the sender computing device can send a message, wherein each message credit account tracks the number of messages sent between the sender computing device and the member of the communications group associated with the message credit account; receiving messages from a plurality of senders that are members of the communications group, wherein the receiving messages comprise receiving packets from the plurality of senders with a transport protocol stack; forming a channel for each sender; and processing messages from each sender in parallel with the corresponding channel, wherein the processing further comprises: sending a message to a receiver that is a member of the communications group; debiting a first message credit account associated with the receiver upon sending the message to the receiver, wherein the receiver maintains a second message credit account associated with the sender computing device; blocking, by the sender computing device, sending messages to any member of the communications group when a balance of the first message credit account is less than or equal to zero; receiving a replenishment message from the receiver, when a balance of the second message credit account falls below a threshold, wherein the replenishment message to increase credits in the first message credit account; resuming sending messages to any member of the communications group when the balance of the first message credit account is greater than zero; and sending the packets marked as Out of Band to an Out of Band thread pool.
 19. The non-transitory machine-accessible storage medium of claim 18 wherein receiving messages further comprises: the transport protocol comprising a multicast receiver thread, a unicast receiver thread, and a connection table.
 20. The non-transitory machine-accessible storage medium of claim 19 further comprising: sending all other packets to a regular thread pool.
 21. An apparatus for processing messages comprising: a memory; a processing device communicably coupled to the memory; an application programming interface (API) executed from the memory by the processing device, the API to receive and send message; a message credit account manager executable from the memory by the processing device, the message credit account manager to: maintain a plurality of message credit accounts that are each associated with a member of a communications group that the apparatus can send a message, each message credit account tracks the number of messages sent between the apparatus and the member of the communications group associated with that message credit account; receive messages from a plurality of senders that are members of the communications group, wherein the receiving messages comprise receiving packets from the plurality of senders with a transport protocol stack; form a channel for each sender; and process messages from each sender in parallel with the corresponding channel, wherein processing the messages further comprises the message credit account manager to: when a message is sent via the API to a receiver that is a member of the communications group, debit the message credit account associated with the receiver of the message wherein the receiver maintains a second message credit account associated with the sender computing device; prevent the sender from sending a message to any members of the communications group when a balance in any of the message credit accounts maintained by the sender becomes negative; credit the message credit account of the sender when a replenishment message is sent to the sender in response to the receiver processing the received message; resume sending messages to any member of the communications group when the replenishment message is received from the receiver; and send the packets marked as Out of Band to an Out of Band thread pool.
 22. The apparatus of claim 21 further comprising: a building block layer communicably coupled to the API; a channel layer communicably coupled to the building block layer; and a transport protocol stack communicably coupled to the channel layer and based on a bidirectional JAVA protocol stack, the transport protocol stack to implement properties specified by the channel layer.
 23. The apparatus of claim 22 wherein the transport protocol stack comprises multicast receiver threads, unicast receiver threads, and a connection table.
 24. The apparatus of claim 22 wherein the transport protocol stack is further to receive messages from a plurality of senders. 